HLA genes are the most polymorphic genes in the human genome. Knowledge about HLA polymorphism in relation to possible peptide-based, T-cell- restricted vaccination protocols is important for understanding the physiology of T-cell recognition and to improve strategies of T-cell antigen-specific vaccination. During the last year the HLA laboratory has developed and perfected techniques for high-resolution typing of HLA class I and class II molecules using polymerase chain reaction (PCR) techniques and comparing the yield and accuracy of information to other techniques, which include directed heteroduplex analysis and automated sequencing of genomic DNA. A combination of these techniques allows more efficient and accurate typing. Multiple new HLA alleles have been discovered in the HLA laboratory last year using this strategy. This will help support peptide-based vaccination protocols ongoing at the NIH. Furthermore, the HLA laboratory has developed a comprehensive method for typing T-cell receptor (TCR) based on Vb-specific, PCR-based amplification and directed heteroduplex analysis, for purposes of screening for TCR clonality. Most recently soluble, epitope restricted HLA tetramer technology and automated sequencing have been perfected which will allow high-resolution/high-efficiency characterization of TCR .These techniques are being utilized for the immunologic monitoring of patients undergoing peptide-based vaccination. in vivo expansion of various relevant T-cell populations in the peripheral circulation and in the area of specific pathologic interest are characterized. The ultimate goal is the identification of the multiple steps occurring in response to T-cell antigen-specific vaccination and their correlation with clinical response.